300tdi conversion and stiff brakes

hello my name is brett,i am from vancouver,b.c.,canada.been reading your forum for quite some time now,picking up tidbits of info
just finished converting my 1997 disco from a petrol v8 to a 300 tdi.runs great lots of power etc.however i get one power assisted brake aplication,then the pedal stiffens up.now i kept the same booster and master cylinder that my v8 used and it all worked fine as a v8.would i then be looking at a new vacuum pump.the lines are intact and it is providing some vacuum,but i am not sure if it is enough.
thanks
brett

wesley64 said:

hello my name is Brett,i am from Vancouver,b.c.,Canada.been reading your forum for quite some time now,picking up titbits of info
just finished converting my 1997 disco from a petrol v8 to a 300 tdi.runs great lots of power etc.however i get one power assisted brake application,then the pedal stiffens up.now i kept the same booster and master cylinder that my v8 used and it all worked fine as a v8.would i then be looking at a new vacuum pump.the lines are intact and it is providing some vacuum,but i am not sure if it is enough.
thanks
Brett

Click to expand...

Hi Brett, are you sure this is a vacuum problem? It sounds a little like air in the braking lines to me, where when you pump the footbrake the pedal hardens up?


Assuming it is as you say a vacuum problem. Did you connect up the vacuum pump on the LHS of the engine (when looking at it in the engine bay) to the servo accumulator? Are you sure the vacuum pump is working correctly? Are you sure there are no leaks,

If you PRESS AND HOLD your foot firmly on the footbrake, then start the engine, what happens?


Dave

thanks for the quick response,dave.yes the vac pump lines are connected properly.i get the same vac from outlet at pump as the hose that connects to the booster.so i assume the line is not leaking.
when i hold my foot firmly on the pedal and start the engine the pedal goes down maybe an inch.
brett

Hey, Im in ontario and recently did the same conversion on my disco. Im having a similar problem as of late. I used to have the abs actuate itself for no reason and then the pedal would be really hard but it would always go back to normal. Now my brakes are rock hard all the time and its hard to stop the vehicle. My vacuum pump is fine and everything else appears to be normal. The brake tests as you described (goes down slightly when i start the engine) and has no audible leaks. I suspect something has happened in my abs modulator but from what ive read that part rarely will cause "hard pedal" problems. Unplugging the power to it does nothing. Anyways im probably going to try getting a new booster/master cylinder to see if it fixes the problem. ill update if I find anything

wesley64 said:

thanks for the quick response,dave.yes the vac pump lines are connected properly.i get the same vac from outlet at pump as the hose that connects to the booster.so i assume the line is not leaking.
when i hold my foot firmly on the pedal and start the engine the pedal goes down maybe an inch.
brett

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Hi Brett, so the pedal is acting normally on engine start.

I had a TDi 300 diesel a while ago that exhibited similar symptoms and I found that when disconnected the electrical supply to the ABS pump (rhs of engine bay) the strange pedal behaviour stopped. So in that case the problem was ABS-related.

Might be worth pulling the ABS electrical connector on yours and testing the brakes. Don't worry you'll still have normal braking, just not the anti-lock function.

Dave

Will do.I will also bleed them again
Brett

And run a diagnostic on the ABS , if fitted , using the blink codes . A search on here will get you all that info but I would stress again the importance of going through the process of clearing all the stored fault codes (details of how to you will find when you search) from previous problems and then reading the blink code again to find the remaining fault(s) .

well i discovered my brake problem.turned out to be the brake booster.luckily i had a spare on the pedal box that the fine gent from the uk sent me when i purchase my engine, trans,etc,etc from him.
funny thing is that the brake booster in the disco, when the v8 was in it, worked fine.i suppose the manifold vacuum in a petrol is more than the vac pump can produce so it managed to do its job even though it was faulty.
thanks for the help
brett

wesley64 said:

well i discovered my brake problem.turned out to be the brake booster.luckily i had a spare on the pedal box that the fine gent from the uk sent me when i purchase my engine, trans,etc,etc from him.
funny thing is that the brake booster in the disco, when the v8 was in it, worked fine.i suppose the manifold vacuum in a petrol is more than the vac pump can produce so it managed to do its job even though it was faulty.
thanks for the help
brett

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That's great news Brett and well done on the conversion overall.

I didn't think you guys bothered much with diesel, is it because of fuel prices?

How much is gas and diesel round your way?

Dave

I love diesel engines and currently own a 2002 dodge ram
whith a 5.9 cummins in it.we just don't have the selection
Of diesel vehicles here that you have.oil company politics.
diesel is 1.44 dollars per liter and petrol is 1.35.I have always
likedd land rovers but the v8 s are pigs on gas.hence the
Coversion.I am going to convert an auto next.the wife refuses
to learn manual.anybody want to sell a 300 with an auto engine
And tranny?
brett

Likewise, changed my booster. Problem solved